The Giant Accreting Protoplanet Survey (GAPlanetS)—Results from a 6 yr Campaign to Image Accreting Protoplanets

Abstract

Accreting protoplanets are windows into planet formation processes, and high-contrast differential imaging is an effective way to identify them. We report results from the Giant Accreting Protoplanet Survey (GAPlanetS), which collected Hα differential imagery of 14 transitional disk host stars with the Magellan Adaptive Optics System. To address the twin challenges of morphological complexity and point-spread function instability, GAPlanetS required novel approaches for frame selection and optimization of the Karhounen–Loéve Image Processing algorithm pyKLIP. We detect one new candidate, CS Cha “c,” at a separation of 68 mas and a modest Δmag of 2.3. We recover the HD 142527 B and HD 100453 B accreting stellar companions in several epochs, and the protoplanet PDS 70 c in 2017 imagery, extending its astrometric record by nine months. Though we cannot rule out scattered light structure, we also recover LkCa 15 “b,” at Hα; its presence inside the disk cavity, absence in Continuum imagery, and consistency with a forward-modeled point source suggest that it remains a viable protoplanet candidate. Through targeted optimization, we tentatively recover PDS 70 c at two additional epochs and PDS 70 b in one epoch. Despite numerous previously reported companion candidates around GAplanetS targets, we recover no additional point sources. Our moderate Hα contrasts do not preclude most protoplanets, and we report limiting Hα contrasts at unrecovered candidate locations. We find an overall detection rate of ∼36 − 22 + 26 % , considerably higher than most direct imaging surveys, speaking to both GAPlanetS’s highly targeted nature and the promise of Hα differential imaging for protoplanet identification.

Systematic Multiepoch Monitoring of LkCa 15: Dynamic Dust Structures on Solar System Scales

“…When the conservative SDI approach is applied, the Hα signalto-noise estimate decreases from 4.9 (in the version with no scaling prior to subtraction) to 2.9 (Follette et al 2023), with the unscaled version closer to the original signal-to-noise ratio published in Sallum et al (2015a). The lower significance of the conservative SDI reduction suggests that scattering from the inner disk at least contributed to the Hα excess.…”

“…The non-SDI Hα and continuum images from Follette et al (2023) show emission at the position of LkCa 15 b at both bands. If we use the reduction in signal-to-noise ratio between the unscaled SDI and scaled SDI (from 4.9 to 2.9) to estimate their relative fluxes, assuming Poisson noise statistics results in an Hα-to-continuum flux ratio of 2.85.…”

“…While the multiepoch ¢ L data sets suggest that forwardscattered light is the source of the NRM signals, the simultaneous detection of LkCa 15 b at Hα in 2014 (e.g., Sallum et al 2015a;Follette et al 2023) is seemingly at odds with this hypothesis. LkCa 15 b's Hα luminosity implies emission in excess of expectations for forward-scattered light, given its contrast in the nearby continuum and the Hα-tocontinuum ratio of the star (which should be the same as the Hα-to-continuum ratio of forward-scattered light).…”

“…In this conservative approach to SDI, any Hα signals with contributions due to forward scattering will have lower significance when Equation (5) is applied. LkCa 15ʼs stellar Hα-to-continuum ratio was measured at 1.81 ± 0.03 in the 2014 observations (Follette et al 2023).…”

“…In the first, continuum images are simply subtracted from Hα images to perform the SDI step. In the second, continuum images are first scaled by the ratio of the stellar fluxes in Hα and continuum (measured via aperture photometry) before being subtracted from Hα observations (e.g., Follette et al 2023).…”